1. Field of the Invention
The present invention relates to an apparatus and method for distributing a fluid specimen onto a test substrate. More particularly, the present invention relates to a dispensing apparatus which employs capillary flow to inoculate a test substrate.
2. Description of Related Art
The art of analytical chemistry has been greatly advanced since biochemistry began emerging as a primary scientific frontier, requiring increasingly sophisticated analytical methods and tools to solve problems. Likewise, the medical profession has lent impetus to the growth of analytical chemistry, with its desiderata of both high precision and speed in obtaining results.
To satisfy the needs of the medical profession as well as other expanding technologies such as the brewing industry, chemical manufacturing, etc., a myriad of analytical procedures, compositions and apparatus have evolved, including the so-called "dip-and-read" type reagent test device. Reagent test devices enjoy wide use in many analytical applications, especially in the chemical analysis of biological fluids, because of their relatively low cost, ease of use, and speed in obtaining results. In medicine, for example, numerous physiological functions can be monitored merely by dipping a reagent strip test device into a sample of body fluid, such as urine or blood, and observing a detectable response, such as a change in color or a change in the amount of light reflected from or absorbed by the test device. Moreover, in light of the increased need for drug testing, reagent strip test devices suitable for inoculating urine chemistry test substrates have become increasing more in demand.
Often diagnostic chemical analysis involves the testing of a single liquid specimen for a multitude of different analytes. Consequently, test devices capable of detecting a multitude of analytes have become available on the market. Illustrative of such test devices currently in use are products available from the Diagnostics Division of Miles, Inc. under the trademarks CLINISTIX, MULTISTIX, KETOSTIX, N-MULTISTIX, DIASTIX, DEXTROSTIX, and others. Test devices such as these usually comprise one or more carrier matrices, such as absorbent paper, having incorporated therein a particular reagent or reactant system which manifests a detectable response, e.g., a color change, in the presence of a specific test sample component or constituent. Depending on the reactant system incorporated with a particular matrix, these test devices can detect the presence of glucose, ketone bodies, bilirubin, urobilinogen, occult blood, nitrite, and other substances. A specific change in the intensity of color observed within a specific time range after contacting the test device with a sample indicates the presence of a particular constituent and/or its concentration in the sample. Some of these devices and their reagent systems are set forth in U.S. Pat. Nos. 3,123,443; 3,212,855; 3,814,668; and 4,647,420. Thus, it is customary for reagent test devices to contain more than one reagent bearing carrier matrix, in which each reagent bearing carrier matrix is capable of detecting a particular constituent in a liquid sample. For example, a reagent test device could contain a reagent bearing carrier matrix responsive to glucose in urine and another matrix responsive to ketones, such as acetoacetate, which is spaced from, but adjacent to, the glucose responsive matrix. Such a product is marketed by the Diagnostics Division of Miles, Inc. under the trademark KETO-DIASTIX. Another reagent test device marketed by the Diagnostics Division of Miles, Inc., N-MULTISTIX, contains eight adjacent reagent incorporated matrices providing analytical measurement of pH, protein, glucose, ketones, bilrubin, occult blood, nitrite, and urobilinogen.
The traditional approach of dipping a reagent strip into a test tube or the like containing the fluid sample was adequate in some instance where there were just a few matrices or pads on the reagent strip. As the number of pads have increased up to as many as 8 to 12 per device to cope with the needs of users, the amount of sample required in a test tube and the size of the test tubes needed to make certain that all of the matrices present on a reagent strip are properly inoculated with test sample have been substantially increased. The need for larger test tubes and higher quantities of fluid sample represents a decrease in economic efficiency as well as an inefficient us of resources. The inefficiency in resources is especially apparent when one considers that in using the dipping approach the sample i contaminated by the first exposure to the first reagent strip. The sample is thus unavailable for further use and must be discarded.
The dipping approach also presents the problem of runover between reagent matrices in which the fluid runover transports chemicals from one matrix to another, resulting in contamination of the matrices and improper results Furthermore, the dipping technique is also a time consuming approach and a messy approach which requires careful blotting of the inoculated reagent test strip following each dipping.
In view of the problems associated with the dipping technique, other techniques have been relied upon. One such technique which the prior art has come to rely upon is the pipetting technique. Pipetting, however, requires a considerable amount of skill with respect to the amount of liquid which is applied to each matrix and the point of application. In addition, and very significantly, the pipetting technique is an extremely time consuming technique which is unsuitable for automatic analysis instruments requirement high throughput. For instance, an auto-urinalysis instrument requires a high throughput (e.g., a minimum of 300 samples/hour) which would mean that the user has about 12 seconds or less for inoculation and syringe cleaning. Pipetting, in itself, requires usually more than 1 second per reagent matrix or pad. Accordingly, pipetting is inappropriate for use with many reading instruments--especially when the reagent strip has a large number (e.g., 8-12) of matrix pads.